Forty children aged 5 to12 years who require endodontic treatment, visiting to the Department of Pediatric and Preventive Dentistry, will be selected for the study who meets the inclusion criteria.

The selected children will be divided into two groups of 20 children each:

Group I: NaOCl without HEBP.

Group II: NaOCl with HEBP.

Following administration of local anaesthesia with 2% lignocaine hydrochloride containing adrenaline at a concentration of 1:80000, isolation of the primary molars will be carried out using rubber dam or with cotton rolls in cases do not permit the placement of clamps for rubber dam isolation. Following isolation, the tooth surface,

rubber dam and clamp will be cleaned with a solution of 3% (v/v) hydrogen peroxide.  The coronal access cavity preparation will be performed using sterile burs (#8 round bur) (Dentsply), and the root canal will be minimally instrumented with K file (Dentsply) and pulp will be extirpated with sterile barbed broach (Dentsply). For each primary molar the largest canal in the upper molar (palatal canal) and lower molar (distal canal) will be selected for the collection of samples from the root canal. The orifice of the remaining canal will be sealed with Cavit (3M ESPE) in order to prevent any possible microbiological contamination during collection of the sample.

For each tooth two samples will be collected in order to assess the microbial count. Sample A: after pulp extirpation and before irrigation (baseline).

Sample B: after irrigation.

A sterile paper point (Metabiomed, India) will be introduced into the full length of the canal and retained in position for 1min to soak up the tissue fluid (sample A).⁶ The collected sample will be placed in sterile Eppendorf tubes containing a nutrient broth and immediately stored in ice box. The canals will be gently cleaned and shaped. The root canal will be alternatively irrigated with the allotted irrigant to the particular group using sterile syringe with 29-gauge side vented needle (NaviTip) after every step of instrumentation. Sample B will be obtained in the similar manner as described earlier after the irrigation.  The treated tooth will be flushed with normal saline to prevent the potential carryover of irrigants. Consequently, a sterile cotton pellet will be placed in the pulp chamber and restored with temporary restoration. The collected samples will be sent to a microbiological laboratory for microbial analysis and microbial colonies will be counted using digital colony counter and expressed as colony forming unit (CFU) per millimetre. The tooth will be subsequently obturated and restored.